The “golden era” of vacuum tube power amplification for guitar, bass and musical instruments may be considered as beginning generally when Mr. Leo Fender developed amplifiers which were essentially copied from early designs offered by RCA and other vacuum tube manufacturers in “app notes” or example designs meant to encourage adoption and application of vacuum tubes. Subsequent designs have mostly been copies of those copies. The result has minimized innovation.
Needs exist for improved audio and musical instrument amplifiers.